Preventing regulator freeze-up

A regulator freeze-up is caused by water in a propane container. Freeze-ups can happen in both horizontal and vertical containers. Water can get into a container in multiple ways.

A new or refurbished container may have some residual water remaining from when a hydrostatic test was performed after it was manufactured or reconditioned. The hydrostatic test ensures the container can withstand pressure. During the test, the container is filled to the top with water and pressurized to look for leaks. Once the test is complete, the container is drained, and the water is evacuated. Most of the time, the water evaporates, but sometimes a bit remains.

Water also can form if the container sits outside overnight in a cool environment with open outlets. The container fills with moist air, and in the morning, with cool temperatures, condensation forms, allowing water to collect in the bottom. Container manufacturers and refurbishers have been working to reduce this, but it still can occur.

It also can be brought in from the propane. Rail cars, transports, bulk plants and delivery bobtails all have the potential to introduce water.

To combat this, methanol, a type of alcohol, is added to the containers and to the propane. Methanol is essentially a dry gas that scavenges the water.

Even with the best efforts, sometimes water remains. When it does, and the propane in the container is near the freezing point of water (32 degrees F), water vapor can leave the container with the propane vapor and pass through a first-stage or twin-stage regulator.

At 30 degrees F, propane in the container is about 50 psi. When it passes through the first stage, the regulator pressure drops from around 50 psi to 10 psi. This pressure drop causes a refrigeration effect. Think about using a compressor to inflate your car’s tire. If you blow air onto your hand, it feels cold. This is because it gives up its latent heat of compression. Fancy term, but in the big picture, if you increase pressure, you increase temperature, and if you decrease pressure, you decrease temperature. We are dropping pressure, and so we are dropping temperature. When the temperature drops below 32 degrees F, the water vapor turns to ice at the regulator’s inlet orifice. That’s where the pressure drop takes place. This drop in temperature and pressure is what causes a freeze-up.

Smaller twin-stage regulators are most susceptible to freeze-ups because they have the smallest Btu and the smallest orifice.

It’s important to note that freeze-ups are a water-in-the-gas issue, not a regulator issue. Regulator manufacturers incorporate design practices to reduce freeze-ups, but by doing so, they are treating the symptoms of the problem, not the problem itself. If water in a container causes a regulator to freeze up, the container needs to be scavenged of water. That means the company needs to take steps to correct the issue.

The Propane Education & Research Council (PERC) has a Battelle report on the use of methanol for controlling water freezing in LPG. The report states that water contamination in propane can cause freezing in valves and regulators, leading to operational issues.

Methanol is widely used as an antifreeze because it prevents water from freezing by forming a low-freezing-point mixture. While effective, excessive methanol can create problems such as corrosion, phase separation and interference with sensitive appliances or engines. The recommended methanol addition is about 600 parts per million (about 4.9 ounces per 100 gallons of propane), balancing freeze protection with minimal risk.

Current field methods for measuring water and methanol are inaccurate; the report recommends developing a non-dispersive infrared-based optical meter for precise, low-cost detection. Additional research is needed on methanol solubility, K-ratios and phase behavior to refine guidelines.

Alternatives to methanol were evaluated, but none matched its effectiveness and cost. Recommendations include developing accurate field-measurement tools, improving industry tracking of methanol addition and avoiding excessive methanol use to prevent corrosion and material issues. Methanol remains the best antifreeze option for propane systems, provided usage is controlled and monitored.

A guide to the use of methanol in propane is available from PERC on its website at bit.ly/perc-battelle.

Randy Warner is product safety manager for Cavagna North America. Reach him at randywarner@us.cavagnagroup.com.

NOTE: The opinions and viewpoints expressed herein are solely the author’s and should in no way be interpreted as those of LP Gas magazine or any of its staff members.

Featured homepage image by Allison Barwacz

---

Related Articles

Understanding certification standards for propane products

Avoid issues with wheel stops and temperature correction

Product certifications: How we know propane products are safe